Cellulose is one of the major components in plant cell wall and is also a major resource of biomass on earth. Hence, many enzymes that degrade cellulose can be widely applied in many different industries. Cellulose is a polysaccharide composed of glucose units linked by β-1,4-glycosidic bond. These polysaccharides organize tightly together to form crystalline cellulose in order to defense external destruction. On the other hand, many kinds of herbivores and microbes need to degrade cellulose from plant to glucose as an energy source by different degrading enzymes including cellulase, xylanase and so on. The catalytic mechanism of cellulase involves hydrolyzing the β-1,4-glycosidic bond between two sugar units by acid-base interaction. Cellulase can be generally divided into three groups including endoglucanase (E.C. 3.2.1.4), cellobiohydrolase (E.C. 3.2.1.91) and beta-glucosidase (E.C. 3.2.1.21). Endoglucanase can randomly degrade cellulose into many small fragments. Cellobiohydrolase can degrade cellulose from reducing end or non-reducing end to release main product, cellobiose. Beta-glucosidase can degrade cellobiose into simple sugar glucose.
Beta-glucosidase widely exists in plants, insects, yeasts, Aspergillus, Trichoderma and bacteria in nature. It participates in the sugar metabolism of organisms and plays an important role in maintaining the normal physiological functions of organisms. Currently, many researches try to obtain better enzymes by either screening in nature or modifying existing enzymes. The present invention intends to analyze the enzyme structure of beta-glucosidase for finding out the key amino acid important to the enzymatic activity, and further modify the enzyme, so as to improve its enzymatic activity and thus increase its industrial value.